The Senate returned the nomination to the White House, effectively killing it,
according to aides to Senate majority leader Harry Reid. ...

Diamond, an MIT professor and expert on taxes and Social Security, faced
opposition from Republicans in the Senate Banking Committee... Richard Shelby,
the committee's top Republican, said Diamond did not have the right sort of
experience for the job.

"I do not believe the current environment of uncertainty would benefit from
monetary policy decisions made by board members who are learning on the job,"
Shelby said before the committee's vote.

The full Senate had been expected to consider Diamond's nomination, along with
those of Janet Yellen and Sarah Raskin, when it returned from its summer recess.
It was unclear whether Obama would resubmit Diamond's nomination or nominate
someone else to fill the post. ...

Update: Here's a bit more clarity on what is happening with the Diamond nomination:

The Senate sent the nomination of Peter Diamond, one
of President Barack Obama’s three nominees for the Federal Reserve
Board, back to the White House because of objections from at least one
lawmaker.

The office of the executive clerk of the Senate
said the procedural move occurred as part of actions taken on nominees
without debate before the chamber left for a summer break. Don Stewart, a
spokesman for Senate Republican Leader Mitch McConnell, said the White
House may resubmit the nomination. ...

Under Senate rules, all nominations that aren’t
completed before a lengthy recess go back to the White House and have to
be resubmitted unless the Senate unanimously agrees to hold onto them
and act later, Stewart said. Routinely, the Senate does agree to retain
the nominations. If a single senator objects, the name goes back
to the president’s office. In Diamond’s case, at least one senator did
that. ...

Update: On Romer's resignation, Tyler Cowen links to:

one commentary, which I cannot vouch for; it concerns a potential clash with Summers.

There's also this and others along similar lines. I didn't link to these accounts for the same reason, I had no way of knowing if it they were accurate. So I can't offer any help on how much weight should be given to the claim that the resignation is due, at least in part, to a clash with Summers.

The Senate returned the nomination to the White House, effectively killing it,
according to aides to Senate majority leader Harry Reid. ...

Diamond, an MIT professor and expert on taxes and Social Security, faced
opposition from Republicans in the Senate Banking Committee... Richard Shelby,
the committee's top Republican, said Diamond did not have the right sort of
experience for the job.

"I do not believe the current environment of uncertainty would benefit from
monetary policy decisions made by board members who are learning on the job,"
Shelby said before the committee's vote.

The full Senate had been expected to consider Diamond's nomination, along with
those of Janet Yellen and Sarah Raskin, when it returned from its summer recess.
It was unclear whether Obama would resubmit Diamond's nomination or nominate
someone else to fill the post. ...

Update: Here's a bit more clarity on what is happening with the Diamond nomination:

The Senate sent the nomination of Peter Diamond, one
of President Barack Obama’s three nominees for the Federal Reserve
Board, back to the White House because of objections from at least one
lawmaker.

The office of the executive clerk of the Senate
said the procedural move occurred as part of actions taken on nominees
without debate before the chamber left for a summer break. Don Stewart, a
spokesman for Senate Republican Leader Mitch McConnell, said the White
House may resubmit the nomination. ...

Under Senate rules, all nominations that aren’t
completed before a lengthy recess go back to the White House and have to
be resubmitted unless the Senate unanimously agrees to hold onto them
and act later, Stewart said. Routinely, the Senate does agree to retain
the nominations. If a single senator objects, the name goes back
to the president’s office. In Diamond’s case, at least one senator did
that. ...

Update: On Romer's resignation, Tyler Cowen links to:

one commentary, which I cannot vouch for; it concerns a potential clash with Summers.

There's also this and others along similar lines. I didn't link to these accounts for the same reason, I had no way of knowing if it they were accurate. So I can't offer any help on how much weight should be given to the claim that the resignation is due, at least in part, to a clash with Summers.